Weed Science 2008 56:457–463
Pronamide Effects on Physiology and Yield of Sugar Beet Kalliopi Kadoglidou, Chrysovalantis Malkoyannidis, Kalliopi Radoglou, Ilias Eleftherohorinos, and Helen-Isis A. Constantinidou* Field experiments were conducted in northern Greece during 2001 and repeated in 2002 and 2004 to evaluate the effects of pronamide on sugar beet. Total leaf area, leaf area index (LAI), leaf and root dry weights, photosynthetic yield (quantum yield of photochemical energy conversion in photosystem II), chlorotic index, and yield components of sugar beet were monitored after pronamide application. Three sugar beet cultivars, ‘Avantage’, ‘Dorothea’, and ‘Bianca’, requiring short, intermediate, and long vegetative periods, respectively, were subjected to treatment. Pronamide was applied on sugar beet either as a double application of 0.63 kg ai ha21 at the two- to four-leaf and 0.63 kg ai ha21 at the four- to six-leaf stage or as a single application of 1.26 kg ai ha21 performed at the latter leaf stage. Both application procedures were combined with a split application of phenmedipham at 0.04 kg ai ha21 plus desmedipham at 0.04 kg ai ha21 plus metamitron at 0.70 kg ai ha21 plus ethofumesate at 0.10 kg ai ha21 plus mineral oil at 0.50 L ha21 applied POST at the cotyledon–to–two-leaf as well as at the four-leaf growth stages. Pronamide (both single and double application) initially caused chlorosis and reduction of sugar beet growth. LAI and photosynthetic yield were also significantly affected for a 2-mo period following the final application, after which the negative effects caused by pronamide were ameliorated. At harvest, sugar beet root and sugar yield, sucrose, K+, Na+, and N-amino acid concentrations were not affected by the herbicide treatments compared with those produced in weed-free and herbicide-free plots, indicating that all cultivars managed to overcome the transient pronamide stress. Regarding sugar beet cultivars, root and sugar yield of Avantage and Dorothea at harvest were higher than that of Bianca, whereas sucrose concentration of Avantage was the lowest. There was not an apparent relationship between the order of sugar yield per cultivar (Dorothea . Avantage . Bianca) and the length of the vegetative period (Avantage , Dorothea , Bianca). Nomenclature: Desmedipham; ethofumesate; metamitron; phenmedipham; pronamide; sugar beet, Beta vulgaris L. ‘Avantage’, ‘Dorothea’, and ‘Bianca’. Key words: Leaf area index, pronamide phytotoxicity, yield.
Dodder (Cuscuta spp.), a member of the Cuscutaceae family, is a nonspecific, aboveground, annual holoparasite, thus totally dependent on its host plant for water supply and assimilation of nutrients. It infects a wide range of plants (crops and weeds), including sugar beet, and causes injury ranging from 23 to 100% (Dawson et al. 1994; Dovas 1975; Jeschke et al. 1994; Sandler et al. 1997). An increasing number of fields around a Hellenic Sugar Industry plant at Platy in northern Greece have been infected by dodder (Cuscuta australis R. Br.) for years. The rapid spread of this weed has been greatly facilitated in this region by growing sugar beet, which is the first host-crop to be sown in spring and the last to be harvested in autumn (Giannopolitis 1979). Control of dodder in sugar beet is presently attempted in Greece with pronamide applied POST. Besides pronamide, soil-applied ethofumesate is also used for dodder control because, according to Giannopolitis (1979), ethofumesate provided greater efficacy against dodder in pot experiments than did pronamide. On the contrary, in petri dish tests pronamide appeared more effective than ethofumesate. Pronamide, a benzamide herbicide, disrupts mitosis in a manner similar to other microtubule disruptors by inhibiting polymerization of tubulin into microtubules. This interference of polymerization is similar to the effect of colchicines or dinitroaniline herbicides (Carlson et al. 1975; Merlin et al. 1987). The net effect of all three categories of chemicals (colchicines are not herbicides) is comparable, inducing a DOI: 10.1614/WS-07-150.1 * First and fifth authors: Laboratory of Agricultural Chemistry, School of Agriculture, Aristotle University of Thessaloniki 54 124 Thessaloniki, Greece; second and fourth authors, Laboratory of Agronomy, School of Agriculture, Aristotle University of Thessaloniki 54 124 Thessaloniki, Greece; third author, National Agricultural Research Foundation, Forest Research Institute, Thessaloniki 570 06, Greece. Corresponding author’s E-mail:
[email protected]
characteristic club-shaped swelling in root tips and other structures that are normally elongated (Carlson et al. 1975; Peterson and Smith 1971). However, pronamide employs a different mechanism. In particular, further ultrastructural and immunofluorescent studies in onion (Allium cepa L.) root tips have revealed that small tufts of microtubules are noted at the kinetochore region of the microtubules (Vaughn and Lehnen 1991), as opposed to the complete absence of microtubules characteristic of the phosphoric amide and dinitroaniline herbicides (Vaughan and Vaughn 1987). Data published on pronamide influence on sugar beet cultivars are limited (Dovas 1975), and limited research has been reported on the effect of some tank-mix POST-applied herbicides on broadleaf weeds encountered in sugar beet fields. Unpublished data collected by the Hellenic Sugar Industry indicated that an early (cotyledon- to two-leaf growth stage) split application of tank-mix POST combinations of phenmedipham plus desmedipham plus metamitron plus ethofumesate was the most effective treatment against broadleaf weeds. Desmedipham, phenmedipham, and metamitron have been reported to be effective inhibitors of the photosystem II (PS II) electron transport (Devine et al. 1993) and ethofumesate as a lipid synthesis (Devine et al. 1993), respiration, and photosynthesis inhibitor (Duncan et al. 1981). Smith and Schweizer (1983) reported a 39 to 55% reduction in sugar beet weight at 45 d after preplant application of cycloate or ethofumesate or ethofumesate plus diclofop, each followed by tank-mix POST of phenmedipham plus desmedipham (0.60 + 0.60 kg ai ha21) applied at 32 d after the preplant application of herbicides. However, sugar beet largely recovered from this early season injury, and root yield reduction at harvest averaged to only 5%. Wilson (1999), also found 10 to 37% leaf area reduction caused by Kadoglidou et al.: Pronamide effects on sugar beet
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Figure 1. Total monthly rainfall (R) and mean monthly temperature (T) recorded at the vicinity of Thessaloniki, northern Greece, during the experimental period (2001, 2002, and 2004).
POST herbicide mixtures, depending on the sugar beet cultivar. At harvest, root yield reduction from herbicide treatments ranged from 3 to 11%. The objective of this study was to investigate the effect of time and rate of pronamide application on physiological responses and yield of three commonly grown sugar beet cultivars in Greece. In particular, herbicide effects on sugar beet were evaluated by determining total leaf area, LAI, leaf and root dry weights, photosynthetic yield (quantum yield of photochemical energy conversion in PS II), and chlorotic index. Root and sugar yields, sucrose, K+, Na+, and N-amino acid concentrations were also measured at harvest. Materials and Methods
Sugar Beet Agronomic Practices. A field experiment was conducted during the 2001 growing season (Yr 1) and repeated in 2002 (Yr 2) and 2004 (Yr 3). The plots were located in different fields each year, but were in the same area near Thessaloniki, northern Greece. Soils were typic xerorthent, i.e. a loamy soil with 0.8% organic matter and a pH of 7.4 in Yr 1, a loamy soil with 1.4% organic matter and a pH of 7.8 in Yr 2, and a clay with 3.0% organic matter and a pH of 8.0 in Yr 3. Mean monthly temperature and rainfall data recorded near the experimental area are given in Figure 1. The experimental fields were plowed in early March and 66 kg N ha21, 40 kg P ha21, and 75 kg K ha21 were incorporated into the soil. The seedbed was prepared by roller harrowing before planting. The three commercial cultivars evaluated were Avantage, Dorothea, and Bianca, requiring short, intermediate and long vegetative periods, respectively. Sugar beet cultivars were planted in 45-cm rows at an approximate density of 83,000 seed ha21. The planting dates were March 16, April 8, and March 23 for Yr 1, Yr 2, and Yr 3, respectively. A split-plot arrangement of treatments was employed in a randomized complete block design with four replicates. The three sugar beet cultivars, with plot size of 2.3 by 35 m, were arranged as main plots, and the four weed management treatments, with plot size of 8 by 2.3 m, were arranged as 458
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subplots. The three main plots were separated by a 2-m wide alley; the four subplots, consisting of six sugar beet rows, were separated by a 1-m wide alley. One of the four weed management subplots remained weed-free and herbicide-free (control) and three received herbicide treatments. The three herbicide treatments consisted of (1) double POST application of the herbicide mixture phenmedipham at 0.04 kg ha21 plus desmedipham at 0.04 kg ha21 plus metamitron at 0.70 kg ha21 plus ethofumesate at 0.10 kg ha21 plus mineral oil at 0.50 L ha21 (HerbMix), performed at the cotyledon–to–two-leaf and at the four-leaf growth stages, (2) HerbMix treatment plus double application of 0.63 kg pronamide ha21 (PrX/X) applied POST at the two- to four-leaf and 0.63 kg pronamide ha21 at the four- to six-leaf growth stages and, (3) HerbMix treatment plus a single application of 1.26 kg pronamide ha21 (Pr2X) applied POST at the four- to six-leaf growth stage. A propane-pressurized hand-held plot sprayer,1 with a 2.4-m-wide boom fitted with six 8002 flat fan nozzles,2 was used and calibrated to deliver 400 L ha21 of water at 250 kPa pressure. Irrigation and other cultural practices were typical of those used for commercial sugar beet production in Greece. All experimental plots (including control) were grown under weed-free conditions (hand weeding in control plots or herbicide application for the rest of the plots), thus assuring that data reflect response to herbicide without any weed competition. Determined Parameters. The effects of herbicide treatments on total leaf area, LAI, leaf and root dry weights, quantum yield of photochemical energy conversion, chlorotic index and, upon harvesting, root and sugar yields (both expressed as Mg ha21), sucrose, K+, Na+, and N-amino acid concentrations were measured. Total leaf area per plant was estimated at 2, 3, and 4 wk after the first herbicide treatment (WAT) on three randomly selected seedlings from the second and fifth rows of each plot. Seedlings were washed and roots were separated from shoots. The leaves of each plant were subdivided into three size categories and the leaves of each category were counted. The area of a representative leaf per category was measured with an LAI-3000 portable leaf area meter.3 Total leaf area per plant was estimated as the sum of the leaf areas of the three categories. Subsequently, roots and leaves per plant were ovendried (48 h, 72 C) and dry weights determined. The LAI was estimated with a plant canopy analyzer4 at 7, 10, 13, and 17 WAT during the 2001 and 2002 growing seasons. In order to avoid underestimation of the crop canopy caused by light reflection off the canopy, measurements were taken from 5:00 A.M. to 7:30 A.M., when light was less intense than later in the day. A 90-degree view cap was installed on the viewing lens to block the operator from the instrument view. The instrument was kept level with soil surface using the bubble level located by the viewing lens. Four readings below the canopy were taken at even intervals, dividing into thirds a diagonal transect spread between the third and the fourth rows of each plot. The first reading was taken adjacent to the crop row, the second at one-third of the way across, the third at two-thirds across, and the last adjacent to the next row. An above-canopy reading was then taken to serve as a reference point for the below-canopy readings. This
Table 1. ANOVA of leaf area and leaf and root dry weights of sugar beet (0, 2, 3, and 4 wk after treatment [WAT]) as affected by cultivara and herbicide treatmentsb during the 2001, 2002, and 2004 growing seasons. Significance of F ratio 0 WAT Source Years Replications Cultivars Year 3 cultivar Error Herbicide treatments Year 3 herbicide treatment Cultivar 3 herbicide treatment Year 3 cultivar 3 herbicide treatment Error Total (df ) CV (%)
2 WAT
3 WAT
4 WAT
df
LAc
LDW
RDW
LA
LDW
RDW
LA
LDW
RDW
LA
LDW
RDW
2 9 2 4 18 3 6 6 12 81 143
** ** NS *
** ** NS NS
** ** NS NS
** NS NS NS
** ** ** NS
** ** NS NS
** ** ** NS
** ** ** NS
** ** NS **
** NS * NS
** NS ** **
** NS NS NS
** NS NS NS
NS NS ** **
NS NS NS NS
** NS NS NS
** ** NS **
** ** ** **
* NS ** NS
** NS ** NS
** NS ** NS
** NS * NS
** NS ** NS
** NS NS NS
4.4
18.5
29.4
4.1
17.5
23.7
4.1
15.1
22.3
2.6
8.4
13.1
a
Sugar beet cultivars: Avantage, Dorothea, Bianca. Herbicide treatments: control, untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two-to four-leaf and 0.63 kg ha21 at four-to six-leaf growth stages); Pr2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four-to six-leaf growth stage). c Abbreviations: CV, coefficient of variation; LA, leaf area; LDW, leaf dry weight; RDW, root dry weight; NS, nonsignificant. * P , 0.05 level of significance; ** P , 0.01 level of significance. b
procedure was performed twice per plot, with LAI and overall averages automatically calculated by the plant canopy analyzer. The chlorophyll fluorescence parameters were recorded at 2, 4, 7, 10, and 13 WAT, using a direct portable fluorometer.5 In each plot, five measurements were taken at the upper third of the canopy of five randomly selected plants on rows three and five. Leaves were of the same physiological age and orientation. Quantum yield of photochemical energy conversion or photosynthetic yield (Fv/Fm values), apparent electron transport rate (ETR), and photosynthetically active radiation were computed, where Fm is the maximal fluorescence, Fo the minimal fluorescence, and Fv the difference between Fm and Fo. The effects of herbicide applications on growth and leaf chlorosis of sugar beet plants was visually estimated using a scale of 0% (no injury) to 100% (complete plant death). Assessments were carried out by three estimators at 2, 5, and 10 WAT. Sugar beet roots from the two 8-m-long center rows of each subplot were hand-harvested at physiological maturity (September 1, October 4, and September 13 in Yr 1, Yr 2, and Yr 3, respectively). Root and sugar yield, sucrose, K+, Na+, and N-amino acid concentrations were measured by the technical department of the Hellenic Sugar Industry. Determination of polarization for determining sucrose concentration was performed according to the macerator or cold aqueous digestion method using leaf acetate as the clarifying agent (method GS621; ICUMSA 2005). Statistical Analysis. Data were combined across growing season, and ANOVA was performed for all measured parameters using MSTAT6 and applying a split-plot factorial approach (sugar beet cultivar by herbicide treatment). The combined analysis of data was justified following the Bartlett’s test for homogeneity of variances, which indicated that data were not heterogeneous. Prior to ANOVA, leaf area, leaf and root dry weights, and LAI data were log(x)-transformed, in order to reduce their heterogeneity. Fisher’s Protected LSD
procedures were used to detect and separate mean treatment differences at P 5 0.05. Results and Discussion
The ANOVA indicated that the leaf area, the leaf dry weight, and the root dry weight were, in most cases, affected by year, cultivar, herbicide treatment, and cultivar by herbicide treatment interaction (Table 1). In most cases, effect of year by herbicide treatment interaction was not significant. Therefore, the means presented in Figure 2 are averaged across years. At 2, 3, and 4 WAT, pronamide applied twice caused the greatest reduction of the above-mentioned three parameters, whereas the application of the mixture of herbicides and the single application of pronamide caused the least reduction, which were significantly different from the controls only at 2 WAT. With regard to differences between cultivars, Bianca showed the highest values of leaf area and leaf dry weight at almost all samplings (Figure 2). Concerning cultivar by herbicide treatment interaction, at 3 and 4 WAT, Bianca was affected more by pronamide applied twice compared with Dorothea, whereas Avantage was the cultivar that suffered the least adverse effect (data not shown). Sugar beet LAI at 7, 10, 13, and 17 WAT was significantly affected by year (Table 2). This is in agreement with results published by Hoffmann and Blomberg (2004), who found that the year and the season in question had a distinct influence on LAI of sugar beet. In addition, at 7 and 10 WAT, LAI was affected by cultivar and herbicide treatments (Table 2). In particular, at 7 WAT, the double application of pronamide caused the greatest reduction of LAI, followed by the single application (Table 3). At 10 WAT, LAI of plants treated with herbicides was significantly lower compared to untreated control. At 13 WAT, the effects on LAI were ameliorated, the sugar beet canopy gradually recovered, and the reduction in LAI from all herbicide treatments was not significant. These results are comparable to those of Wilson (1999), who found that application of ethofumesate plus phenmedipham plus desmedipham, (0.16 + 0.16 + Kadoglidou et al.: Pronamide effects on sugar beet
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Figure 2. Leaf area and leaf and root dry weights of sugar beet as affected by four herbicide treatments (A) and three sugar beet cultivars (B) at 2, 3, and 4 wk after treatment (WAT). Means are averaged over (A) 3 yr and three cultivars and (B) 3 yr and four treatments. Different letters characterize significant differences between (A) treatments or (B) cultivars for each WAT evaluation (according to the Fischer’s Protected LSD test at the 5% level). Treatments included the following: control: untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two- to four-leaf and 0.63 kg ha21 at four- to six-leaf growth stages); Pr 2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four- to six-leaf growth stage). Cultivars: Avantage, Dorothea, Bianca.
Table 2. Analysis of variance of leaf area index of sugar beet as affected by cultivara and herbicide treatmentsb during the 2001 and 2002 growing seasons at 7, 10, 13, and 17 wk after treatment (WAT). Significance of F ratio WAT Source
df
7
10
13
17
Years Replications Cultivars Year 3 cultivar Error Herbicide treatments Year 3 herbicide treatment Cultivar 3 herbicide treatment Year 3 cultivar 3 herbicide treatment Error Total (df ) CV (%)
1 6 2 2 12 3 3 6 6 54 95
** ** * NS
** ** * **
** NSc NS NS
** NS NS NS
** ** NS NS
** NS NS NS
NS NS NS NS
NS NS NS NS
12.7
a
10.3
18.1
15.6
Sugar beet cultivars: Avantage, Dorothea, Bianca. Herbicide treatments: control, untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two-to four-leaf and 0.63 kg ha21 at four-to sixleaf growth stages); Pr2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four-to six-leaf growth stage). c Abbreviations: CV, coefficient of variation; NS, nonsignificant. * P , 0.05 level of significance; ** P , 0.01 level of significance. b
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0.16 kg ha21), reduced sugar beet LAI at 9 WAT by 22% compared to controls, at 11 WAT by 15%, and at 13 WAT by 3%. At 17 WAT, sugar beet canopy had recovered so the reduction in LAI from herbicide treatment was not evident (0%). Sugar beet cultivars reportedly respond differently to herbicide treatments (e.g., Smith and Schweizer 1983). In the present experiment, LAI among different sugar beet cultivars ranged from 1.5 to 3.05 m2 m22 (Table 3), values falling in the range reported by others, but lower than previously recorded optima. For example, Wilson (1999) and Hoffmann and Blomberg (2004) reported LAI between 0.32 and 7.5 m2 m22, and Ro¨ver (1994) and Scott and Jaggard (1978) found optimal LAI for sugar beet in summer of about 3.5 to 4.0 m2 m22. Sugar beet photosynthetic yield was affected at 2 WAT by year, cultivar, and herbicide treatment (Table 4). Thereafter, photosynthetic yield was mainly affected by herbicide treatments, thus means presented are averaged across years and cultivars (Figure 3A). Both applications of pronamide (double and single) significantly decreased photosynthetic yield of sugar beet up to 10 WAT compared to control plants, whereas the herbicide mixture resulted in less photosynthetic yield only up to 4 WAT (Figure 3A). Plants were progressively recovering as the growing season proceeded, and photosynthetic yield was consistent across all treatments at 13 WAT. Regarding differences among cultivars, all cultivars exhibited the same photosynthetic yield across evaluations except Dorothea, which had a significantly lower photosynthetic yield at 2 WAT (Figure 3B). These results are in agreement with those reported by Ro¨ver (1998), who found that certain herbicides, expressing their adverse effects through chlorophyll fluorescence, caused only temporary inhibition of the physiological function of sugar beet photosynthesis. The visual assessment data (i.e., reduction of sugar beet growth and chlorosis expressed as a percentage of the control) Table 3. Leaf area index (LAI) of sugar beet as affected by herbicide treatments (averaged across three cultivars and 2 yr) and by cultivars (averaged across 2 yr and four herbicide treatments) at 7, 10, 13, and 17 wk after treatment (WAT). Data before the ANOVA were log(x)-transformed, but means presented are backtransformed. LAI at WAT Treatment Herbicidesa Control HerbMix PrX/X + HerbMix Pr2X + HerbMix Cultivar Avantage Bianca Dorothea
7
10
13
17
-----------------------------------m2 m22 ---------------------------------1.9 1.9 1.6 1.6
ab a b b
1.6 b 1.8 a 1.8 a
3.3 2.9 2.9 2.7
a b b b
2.8 b 3.0 ab 3.1 a
1.8 1.6 1.8 1.5
a a a a
1.5 b 1.8 a 1.7 ab
1.6 1.5 1.5 1.5
a a a a
1.5 a 1.6 a 1.6 a
a Herbicide treatments: control, untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two-to four-leaf and 0.63 kg ha21 at four-to sixleaf growth stages); Pr2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four-to six-leaf growth stage). b Herbicide or cultivar means within the same column followed by the same letter are not significantly different according to Fischer’s Protected LSD test at the 5% level.
Table 4. Analysis of variance of photosynthetic yield, at 2, 4, 7, 10, and 13 wk after treatment (WAT) and of root and sugar yield, sucrose, K+, Na+, and N-amino acid concentrations of sugar beet at harvest as affected by cultivara and herbicide treatmentsb during the 2001, 2002, and 2004 growing seasons. Significance of F ratio WAT Source Years Replications Cultivars Year 3 cultivar Error Herbicide treatments Year 3 herbicide treatment Cultivar 3 herbicide treatment Year 3 cultivar 3 herbicide treatment Error Total (df ) CV (%)
Harvest
df
2
4
7
10
13
RYc
SC
SY
[K+]
[Na+]
[a-N+]
2 9 2 4 18 3 6 6 12 81 143
** ** ** NS
** NS NS **
** ** NS NS
** NS NS NS
** NS NS NS
** NS ** *
** NS ** NS
** ** ** NS
** NS ** **
** NS ** **
** NS ** NS
** NS NS NS
** NS NS NS
** NS NS NS
** NS NS NS
NS NS NS NS
** NS NS NS
NS NS NS NS
** NS NS NS
NS NS NS NS
NS NS NS NS
NS NS NS NS
13.7
10.0
9.9
11.1
12.1
7.4
3.9
8.0
4.8
14.5
12.1
a
Sugar beet cultivars: Avantage, Dorothea, Bianca. Herbicide treatments: control, untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two-to four-leaf and 0.63 kg ha21 at four-to six-leaf growth stages); Pr2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four-to six-leaf growth stage). c Abbreviations: CV, coefficient of variation; RY, root yield; SC, sucrose concentration; SY, sugar yield; [a-N+], N-amino acid concentration; NS, nonsignificant. * P , 0.05 level of significance. ** P , 0.01 level of significance. b
also indicated that sugar beet cultivars exhibited a similar response to herbicide treatments, which did not vary among years (data not shown). At 2 WAT, the double application of pronamide caused the greatest reduction of sugar beet growth
Figure 3. Photosynthetic yield of sugar beet as affected by (A) four herbicide treatments and (B) three sugar beet cultivars at 2, 4, 7, 10, and 13 wk after treatment (WAT). Means are averaged over (A) 3 yr and three cultivars and (B) 3 yr and four treatments. Different letters characterize significant differences between (A) treatments or (B) cultivars for each WAT evaluation (according to the Fischer’s Protected LSD test at the 5% level). Treatments included the following: control: untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two- to four-leaf and 0.63 kg ha21 at four- to six-leaf growth stages); Pr 2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four- to six-leaf growth stage). Cultivars: Avantage, Dorothea, Bianca.
(22% of the untreated control), followed by the single application of pronamide (9% of the untreated control). At 5 WAT, growth inhibition and chlorosis due to herbicide treatments was less than 5%, whereas at 10 WAT, the percentage was less than 2%, indicating that sugar beet managed to overcome the pronamide negative effect. In general, the toxic symptoms caused by the herbicides were limited and the recovery period of plants was shorter in comparison to other cultivars previously studied (Smith and Schweizer 1983; Wilson 1999). Potassium (K+), Na+, and N-amino acid concentrations were affected only by year and cultivar, whereas herbicide treatments did not have any effect (Tables 4 and 5). Potassium and Na+ concentrations of Avantage were higher than those of Dorothea and Bianca, whereas the N-amino acid concentration of Avantage and Bianca was higher than that of Dorothea. There was an overall significant influence of year, cultivar, and herbicide treatments upon root and sugar yield parameters (Table 4). With respect to herbicides, root and sugar yield was not reduced by pronamide treatments compared with the control, but a 5.0 and 6.6% increase in root and sugar yield was respectively provided by the herbicide mixture compared to control (Table 5). This indicates again that the herbicide treatments did not have any adverse effect on sugar beet. A greater root yield was apparent in all treatments than in the control. Possible mechanical damage due to hand weeding applied on control crop plants could be the reason for this sugar and root yield trend. These results are in contrast to those of Smith and Schweizer (1983), who found that application of desmedipham plus phenmedipham (0.60 + 0.60 kg ha21), applied once POST on several cultivars of sugar beet, reduced root yield in two experimental growing seasons by 4.4 to 5.7%. In addition, Wilson (1999) also found that two POST applications of desmedipham plus phenmedipham plus ethofumesate (0.16 + 0.16 + 0.16 kg ha21) reduced root yield of several sugar beet cultivars by 6%. Sucrose concentration was not affected by pronamide and herbicide mixture treatments compared to the Kadoglidou et al.: Pronamide effects on sugar beet
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Table 5. Root and sugar yield, sucrose, K+, Na+, and N-amino acid concentrations at harvest as affected by herbicide treatments (averaged over 3 yr and three cultivars) or by sugar beet cultivars (averaged over 3 yr and four herbicide treatments). Evaluated parameter Treatment
Root yield
Sucrose concentration
Sugar yield
Mg ha21
%
Mg ha21
bc a ab b
13.0 13.2 13.2 13.2
[K+]
[Na+]
[a-N+]a
---------------------------meq 100 g21 --------------------------
b
Herbicides Control HerbMix PrX/X + HerbMix Pr2X + HerbMix Cultivar Avantage Bianca Dorothea
94.8 99.5 96.9 95.3
101.2 a 91.4 b 97.3 a
a a a a
12.3 13.1 12.7 12.5
12.7 b 13.3 a 13.5 a
b a ab b
12.7 a 12.1 b 13.1 a
4.7 4.8 4.8 4.8
a a a a
4.9 a 4.7 b 4.7 b
2.7 2.6 2.7 2.6
a a a a
3.1 a 2.5 b 2.4 b
3.2 3.1 3.1 3.2
a a a a
3.2 a 3.3 a 3.0 b
Abbreviations: [a-N+], N-amino acid concentration; meq, milliequivalents. Herbicide treatments: control, untreated plants; HerbMix, herbicide mixture: double POST application of phenmedipham (0.04 kg ha21) plus desmedipham (0.04 kg ha21) plus metamitron (0.70 kg ha21) plus ethofumesate (0.10 kg ha21) plus mineral oil (0.50 L ha21) at cotyledon–to–two-leaf and at four-leaf growth stages; PrX/X: HerbMix plus pronamide double application (0.63 kg ha21 applied POST at two-to four-leaf and 0.63 kg ha21 at four-to six-leaf growth stages); Pr2X: HerbMix plus pronamide single application (1.26 kg ha21 applied POST at four-to six-leaf growth stage). c Herbicide or cultivar means within the same column followed by the same letter are not significantly different according to Fischer’s Protected LSD test at the 5% level. a
b
control (Table 5). In addition, sugar yield was not affected by pronamide treatments compared to the control but a 6.6% increase was recorded in plants treated with the herbicide mixture. These findings further add to the conclusion that full recovery of plants was obtained after herbicide application. Root and sugar yields of Avantage and Dorothea at harvest were higher than that of Bianca, whereas sucrose concentration of Avantage was the lowest of all three (Table 5). There was not an apparent relationship between the order of sugar yield per cultivar (Dorothea . Avantage . Bianca) and length of vegetative period (Avantage , Dorothea , Bianca). The observed negative correlation between sucrose concentration and root yield, more prominent in Avantage, was expected because of a dilution effect. The correlation factor for sugar concentration and root yield was r 5 20.63 (data not shown). This is in agreement with results from Bosemark (1993), who also found a negative correlation factor (r 5 20.68) in experiments with 17 sugar beet cultivars. The results of this study showed clearly that the POSTapplied pronamide has the potential to injure sugar beet immediately after application. In particular, pronamide negatively affects all the physiological parameters examined in early season. An interesting finding of this research is the subsequent progressive recovery of sugar beet plants until harvest, eliminating any root or sugar yield reduction. The recovery mechanism may involve herbicide detoxification and a subsequent stimulatory effect involving rapid cell division, elongation, or both (Kiermayer 1964). As mentioned earlier, dodder competition with sugar beet can cause an immense yield loss, much greater than the primary injury caused by pronamide. Therefore, control of dodder with pronamide should be more profitable than allowing dodder to compete with the crop.
Sources of Materials 1
AZO sprayer, propane-operated knapsack, and field plot sprayer, Veeze–Ede-Konstrukties, P.O. Box 350-6710 BJ EDE, The Netherlands. 2 Teejet Spray System Co., P.O. Box 7900, Wheaton, IL 60188. 3 LAI-3000 portable leaf area meter, LI-COR, Inc., 4421 Superior Street, Lincoln, NE 68504.
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LAI-2000 Plant canopy analyzer, LI-COR, Inc., 4421 Superior Street, Lincoln, NE 68504. 5 Photosynthesis yield analyzer MINI-PAM, portable chlorophyll fluorometer, Walz, Effeltrich, Germany. 6 MSTAT-C, a microcomputer program for the design, management, and analysis of agronomic research experiments. Crop and Soil Sciences Department, Michigan State University, East Lansing, MI 48824.
Acknowledgments The authors gratefully acknowledge the support of Hellenic Sugar Industry and the contribution of George Apostolidis and Philippe Ioannidis, then General Director and Chief of Research of Hellenic Sugar Industry, respectively, in the realization of this work. The authors also thank Evangelos Kaitsiotis, Efstathia Konstantinou, and Gregorios Morakis for their assistance in conducting part of the studies and the reviewers for their constructive remarks.
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Received September 13, 2007, and approved February 1, 2008.
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